Polymers: Quality Control

Polymer-based products are found in almost any industry and are prevalent in modern consumer products. The degree of variability in polymer formulations allows polymer properties
to be easily altered to
best fit an end-use requirement. Characteristics like average molecular weight, degree of cross-linking, and chemical composition all affect the ultimate physical properties of the polymer. Even slight variations in temperature, pressure, and feed ratios in the production and processing steps can affect the final polymer properties. Because of this, it is necessary to frequently test raw materials, process equipment, and the final products to ensure specifications are being met.

(Copyright Milacron, Batavia, OH)

Process Map

Importance of Quality Control

Quality control is an essential component of a successful company or industry. It guarantees that all products meet or exceed internal specifications and the expectations of consumers.
It further reduces waste and inefficiencies within a process.
If all components of a process are held to the highest quality and all pieces of equipment are regularly calibrated, then the risk of product failing quality control measures is minimized and no material would be disposed of.

Strict quality control practices are paramount to maintaining reputation within an industry. Customers often share opinions of products amongst one another and positive reviews can sway other potential consumers, whereas negative opinions of product quality can be extremely detrimental to sales and marketing efforts. If consumers perceive a product to be of a higher quality, then they are more likely to remain loyal to that company who produced the product. Thus, if a company wishes to remain competitive, it is important to implement good quality control practices.

Quality Control Test Batteries

There are a multitude of ways in which quality control is implemented in a process. Commonly, though, there are in-line and end-of-line quality control measures that are used.

In-Line Testing

In-line quality control
relies on some sensor technologies
and technicians who operate the equipment producing polymer components. These technicians generally perform visual inspections and remove any notably defective finished pieces. Additionally the technicians can be provided with simple pieces of equipment to test product quality, such as gages. When using a gage, a technician places the processed polymer product into a pre-constructed guide to make sure the product meets the shape and dimension specifications. Technicians might perform this test on every 10th component, as advised by the quality control department.
Technicians might also be asked to test raw material resins for moisture content or other contaminants prior to its introduction to the process.

There are additional in-line advanced process controls that can be implemented on various pieces of process equipment. While sensors have been developed that can be applied to the determination of polymer properties, they have only really been applied to laboratory-scale process equipment. As such, an inferential system can be used to communicate more easily measurable process variables like temperature, pressure, and flow rates, using a computer model to correlate polymer properties to these variables. These computer models are developed by the quality control or research and development departments and undergo constant adjustment and re-calibration based on the real properties of the polymer once it’s reached the end-of-line.

End-of-Line Testing

Once a product has reached the end-of-line of a process and is ready to be shipped to customers, other quality control tests can be performed to ensure production runs performed adequately to meet specifications. These end-of-line quality control tests are typically performed by a company’s quality control department guided by standard operating procedures (SOPs) for specific quality control equipment and instruments. These batteries of tests can vary in intensity depending on the end use of the polymer, but common physical properties tested can include tensile strength, burst strength, thermal and electrical conductivity/resistance, adhesion strength if products are multilayer polymer systems, and permeability if fluids are flowing along the polymer. These tests may be repeated at different temperatures, pressures, and chemical environments to simulate operating conditions for the final product.